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01-07-2015, 10:44 PM   #1
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write speed

I think this might have been done to death, but I am totally bamboozled by the slow shutter speed write time. Thirty seconds is fine, and I get instant view. the moment I go to bulb and over 30 seconds, the 'gears' start whirring away. I have turned of the NR for slow shutter speed to no avail. Yesterday I put the setting to bulb and went out in daylight and exposed for 40 seconds, just to see what would happen. Well, off went the gears again, and years later the image appeared on the screen. (yes it was blown out but that didn't matter). I wonder why in daylight it has the same problem, if there is no black for it to read. (as it is explained that the buffer thingy is reading the black during that hideous write reading). What I also don't understand is this: last year we went to a light show. The fellows said turn off the NR which we all did. Not one of the exposures took time to read, and I had instant images, so I was all ready for the next shot. Here is an image which was exposed for 44 seconds. We also did some star trails, and painted trees with laser lights. All were exposed for more than 30 seconds. I just cant work out what I did then, that I obviously am not doing now. The image below was at 100 iso f11 on 'pattern'. I assume the latter is the metering? I am using a Sandisk extreme pro, which is the same card as used in the image below.
So if anyone can shine some light on this, (ha ha) I would be most appreciative.

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PENTAX K-7  Photo 

Last edited by trishytee; 01-07-2015 at 10:49 PM. Reason: To add
01-07-2015, 11:50 PM   #2
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QuoteOriginally posted by trishytee Quote
(as it is explained that the buffer thingy is reading the black during that hideous write reading)
The buffer isn't the culprit here. If the noise reduction were really off, the file should save the be shown almost instantly. Otherwise, you'll have to wait for the same number of seconds as the original exposure.

To the best of my knowledge nothing else can cause such a long delay.

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01-08-2015, 12:20 AM   #3
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QuoteOriginally posted by Adam Quote
The buffer isn't the culprit here. If the noise reduction were really off, the file should save the be shown almost instantly. Otherwise, you'll have to wait for the same number of seconds as the original exposure.

To the best of my knowledge nothing else can cause such a long delay.
I just double checked, Adam. I have 18 and 19 turned off. 18 being 'slow shutter release noise reduction' and 19 being 'High ISO Noise Reduction' under 30 seconds instant file shown, at 50 secs I had to wait for the same 50 seconds for the file to show. I tried it again, with 19 in normal mode, but still no luck. so I am at a complete loss here. Looks like I won't be doing any more moonlight shots! sob
01-08-2015, 01:38 AM   #4
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QuoteOriginally posted by trishytee Quote
(as it is explained that the buffer thingy is reading the black during that hideous write reading
Actually, the camera is taking another photo with the shutter closed. It's not "reading the black" in your image.

01-08-2015, 04:45 AM   #5
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QuoteOriginally posted by Giklab Quote
Actually, the camera is taking another photo with the shutter closed. It's not "reading the black" in your image.
Well whatever it is doing what is the solution. Plus why do that if I take the photo in daylight, being no noise problem??

Last edited by trishytee; 01-08-2015 at 04:46 AM. Reason: forgot last part
01-08-2015, 05:01 AM   #6
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The noise is due to heat buildup in the sensor for a long time, not the light levels of the picture subject. The second shot is used for comparison and correction.
01-08-2015, 05:08 AM   #7
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Ahhh, well that explains that little exercise, but it seems I am stuck with never being able to do long exposures without losing a lot of time. It is horrible when I go with my Cannon mates and they are clicking away, while I miss several lightning strikes waiting for this buffering. I found this on another site:
Well the K7 only allows the noise reduction to be turned off for exposures under 30 seconds, and in my experience doesn't matter what camera or sensor, not having the Noise reduction makes the shots unusable, like would have been cleaner using 25600 ISO kind of unusable".
Does anyone know if the K3 is any better. I wish Pentax would get rid of the buffering and let us worry about our noise. I would hate to change cameras now as I have so many lenses etc, but this really does become painful on night shoots.
01-08-2015, 05:18 AM   #8
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If it really troubles you, a second K-7 must cost almost nothing and would multiply your work flow options.

01-08-2015, 05:22 AM   #9
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QuoteOriginally posted by clackers Quote
If it really troubles you, a second K-7 must cost almost nothing and would multiply your work flow options.
Not sure I understand that message Clackers? How would that help with my noise problem? I shall look for more edification here tomorrow night. Now 8.20 Pm in Perth. I am off to work. I suppose if I up my ISO I could get away with under 30secs, but the pictures seem sharper on 100, or is that my imagination.
01-08-2015, 05:23 AM   #10
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???

Open the shutter on the second while the first is processing.
01-08-2015, 06:26 AM   #11
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The phenomenon you experience is called "dark frame subtraction". It's a long exposure noise reduction technique lifted from astronomy.


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01-08-2015, 08:42 AM   #12
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I don't have a k-7, but it looks like the dark frame subtraction can't be turned off for exposures longer than 30 seconds. There are a few threads about it https://www.pentaxforums.com/forums/6-pentax-dslr-discussion/66277-k7-long-exposures.html. It can be completely disabled on the k5 series, I'd guess on the k3 as well but double check on that if you're going for an upgrade.

You could take multiple 30 second exposures and stack later in post processing.
01-08-2015, 12:15 PM - 1 Like   #13
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Checking the manuals, it looks like your camera is the last model where it could not be completely switched off; K-r and K30 (safe to assume K50 as well) and K5 (safe to assume successors as well) all can switch it off completely.

Download the manuals and check the slow shutter speed options.
01-08-2015, 10:56 PM   #14
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QuoteOriginally posted by sterretje Quote
Checking the manuals, it looks like your camera is the last model where it could not be completely switched off; K-r and K30 (safe to assume K50 as well) and K5 (safe to assume successors as well) all can switch it off completely.

Download the manuals and check the slow shutter speed options.
Correct. You cannot turn off DFS on the K7, but you can on the K5. If long exposures are truly what the OP is after, then it may be time for an upgrade. K5's are pretty cheap now.
01-09-2015, 04:30 AM   #15
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Same write speed characteristic on the K20D. Makes long exposures at sunrise and sunset challenging 'cause you only have half the time to sort your settings out. Faster cards only make a marginal difference.
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